In the field of mobile communication systems, particularly cellular communication systems, one issue relates to cell search and synchronization. Such cell search and synchronization is to be performed by any terminal for connecting to a cellular system and for ensuring terminal mobility within a cellular system, i.e. a cell thereof, either when powering up the terminal or when transiting from an idle mode to a connected mode or when transiting from one cell to another cell.
The speed with which cell search and synchronization can be performed by a terminal is important for both end-user experience and the resulting power consumption of the terminal. For the end user, increased synchronization time and power consumption means reduced standby time and significantly prolonged establishment of the cellular connection with the cellular system. Therefore, the (initial) cell search and synchronization is an important aspect of the network performance and end-user experience. This is why it is typically considered to be critical to ensure that the terminal's (initial) synchronization time is a low as possible as well as the idle mode power consumption.
Conventionally, cell search and synchronization procedures typically rely on a power-based ranking of carrier signals being broadcasted on specific carriers (such as synchronization signals being broadcasted on specific synchronization channels), which are received at a terminal trying to re-/connect to a cellular system. Specifically, it is known that the terminal calculates RSSI measures for available carrier signals of specific carriers, ranks the carriers based on the RSSI measures thereof, and executes a cell search and synchronization procedure based on the carrier ranking starting with the carrier having the highest ranking.
Such conventional cell search and synchronization procedures are efficient in terms of synchronization time and power consumption as long as it is ensured that all available (i.e. received) carriers or carrier signals are relevant for the cell search and synchronization purpose. Hence, such conventional cell search and synchronization procedures are sufficient in deployment scenarios in which only a single cellular system operates on a specific frequency range/band which is monitored by terminals for connecting to this cellular system.
However, in recent and future mobile communication systems, particularly cellular communication systems, there will increasingly be in practice deployment scenarios in which multiple cellular systems operate on a specific frequency range/band. For example, such deployment scenarios are resulting from 3G frequency re-farming activities, e.g. the introduction of WCDMA services on the GSM band, LTE frequency re-farming activities, and the like. Hence, a terminal in such deployment scenario is likely to experience networks with one or more of GSM, 3G, 3.5G, CDMA, WCDMA, TD-SCDMA, and LTE/LTE-A carriers co-existing in a specific frequency range/band.
Such deployment scenarios are problematic in terms of efficiency of conventional cell search and synchronization procedures. This is essentially because the carriers and carrier signals may not be distinguished regarding their origin from or belonging to a specific cellular system. Hence, the RSSI-ranked carrier list will be disrupted by carriers of non-desired cellular systems, i.e. those cellular systems which the terminal does actually not desire to connect to. As a result of such disrupted conventional RSSI ranking, the terminal may firstly attempt to execute a cell search and synchronization procedure based on a carrier which originates from or belongs to a cellular system other than that desired to be connected to. Such attempt will naturally fail, and a further attempt of cell search and synchronization will have to be executed based on the next carrier in the ranking, until a relevant carrier of the desired cellular system is reached.
When assuming that the available carriers distinctively belong to coexisting 2G and 3G network, such disruption goes in both directions, i.e. a terminal synchronizing to a BS/BTS in a network containing both 2G and 3G carriers on the same frequency band will be impacted both when attempting synchronization to the 2G network and to the 3G network. Having additional carriers for other cellular systems will further increase such disruptions.
Accordingly, every time the terminal attempts to synchronize to a non-desired cellular carrier, it wastes synchronization time and idle mode power.
Therefore, the application of conventional cell search and synchronization procedures in deployment scenarios with multiple carriers from different cellular systems coexisting in a given frequency range/band will adversely result in increased synchronization time and power consumption.
In view thereof, there exist problems in terms of efficiency (e.g. regarding synchronization time and power consumption) in the context of cell search and synchronization in a cellular system, in particular in a deployment scenario in which multiple carriers of different cellular system coexist within the same frequency range/band.
Thus, there is a need to further improve cell search and synchronization in a cellular system.